The present application relates to spectacles, spectacle frames and methods for providing spectacles of the wrap-around type, and, in particular, to frames adapted to receive optical lenses characterized by contour fitting with changes in base curvature across the lens.
It is known in the prior art to manufacture non-corrective eyeglasses such as sunglasses or protective eyeglasses having wrap-around segments designed to shield the eye from incident light, wind, and foreign objects in the temporal vision field of the wearer.
Visible light and light in the UV region may enter the eye from angles as high as 100xc2x0 from the line of sight. There has been a need to provide sunglasses or protective eyeglasses, with a significant range of refractive powers, whilst maintaining a cosmetically acceptable appearance. The high radius of curvature required for a properly aligned ophthalmic lens including a prescription surface to enclose the wearer""s eyes is such that the spectacles would produce a bug-eyed appearance, which would be cosmetically unacceptable. Fashionable eyewear incorporating wide field spherical lenses of very high curvature, such as those disclosed in U.S. Pat. No. 6,142,624 to Applicants, are positioned close to the eyes to enclose the visual field of the wearer whilst maintaining alignment of the optical axes with the direct line of sight. As disclosed in this patent frames for such lenses may be designed to lie on an extension of a spherical front surface thereof.
Applicants disclose in International Patent Application PCT/AU97/00188 xe2x80x9cImproved Single Vision Lensesxe2x80x9d (now U.S. Pat. No. 6,361,166), an optical lens element including a front and back surface, at least one surface being continuous, and forming a prescription (Rx) zone and a peripheral temporal zone for providing a shield in the area of the temples, which zones are smoothly blended to avoid a prismatic jump from the Rx zone to the temporal zone. These lenses are designed to be located before the wearer""s eyes so that the direct line of sight intersects the optical center of the lens front surface, but the optical axes are rotated temporally in order to assist achievement of the wrap-around configuration. Such lenses have surface corrections in order to reduce optical errors within the field of vision as a result of the intended horizontal tilt.
In International Patent Application PCT/AU98/00274 xe2x80x9cLenses and Spectacles Bearing Lensesxe2x80x9d (now U.S. Pat. No. 6,334,681), to Applicants, the entire disclosure of which is incorporated herein by reference, Applicants disclose an ophthalmic article including an optical lens element having a front and back surface, at least one surface being continuous, and forming a prescription (Rx) zone and optionally a non-prescription peripheral temporal zone, at least one surface exhibiting a change of base curve across the field of vision of the wearer; the front and/or back surface bearing a surface correction to at least partially adjust for optical errors. The curvature changes accentuate the lens surface shape in order to fit the contour of the wearer""s face and minimize the need for tilt.
Whilst such lenses provide lens design options not heretofore available, it is necessary to provide spectacle frames for such unusually shaped lenses.
Applicants have investigated the topological properties of surfaces with changing base curve across a desired aperture, investigating in particular the opportunity to maintain a simple geometric form for the carrier surface on which the lens aperture is formed, despite the complexity of the surface to be intersected by the frame outline.
Most eyeglass lenses and frames are formed on spherical, cylindrical or toroidal xe2x80x9ccarrier surfacesxe2x80x9d, meaning that the aperture outlines of the lens and the frame may be formed on a simply defined surface that is proximate the physical surface of the lens being glazed. For non-corrective lenses, the carrier surfaces and the lens front surface are usually coincident. Wrap around shields and unitary lenses may employ elliptic or high order polynomial surface forms. In this case, the lens outline is typically formed directly on the lens surface and the difficulties presented in creating a closed lens aperture are avoided by using temple bar or rimless forms of lens support. See for example U.S. Pat No.: 1,741,536 (Rayton); U.S. Pat. No. 4,859,048 (Jannard); U.S. Pat. No. 4,867,550 (Jannard); U.S. Pat. No. 5,604,547 (Davis); U.S. Pat. No. 5,774,201 (Tackles); U.S. Pat. No. 5,689,323 (Houston et al.) and; U.S. Pat. No. 5,825,455 (Fecteau et al.).
The design of prescription lenses is complicated by the need to eliminate optical errors in the oblique visual field. Specifically, the lens designer needs to observe a relationship between front surface curvature and lens through power specified by the so-called xe2x80x9cTscheming Ellipsesxe2x80x9d first described 100 years ago. These identify specific combinations of frontal base curvature and Rx power that minimize oblique astigmatic and/or power errors as shown below. See, M. Jalie, The Principles of Ophthalmic Lenses p. 418-422 (4th Ed. London, 1994).
Such xe2x80x9cbest formxe2x80x9d lenses have front surfaces that are consistently steeper as the Rx becomes more positive. When referred to a fixed aperture, the front vertex height (plate height) also increases as the Rx becomes more positive. Accordingly a range of typical prescription lenses has a range of different front surfaces. It is an objective to accommodate a full range of Rx values with a single frame to a given style. It follows that even for simply formed prescription lenses, the frame carrier surface and the lens carrier surface will be coincident in one part of the prescription range only.
It is impractical in the design of frames for conventional prescription lenses to make the frame carrier surface coincident with the front surface of the lens it retains, unless the frame is of a temple bar or rimless style. An exception to this occurs for a specific group of very highly curved lenses wherein a range of different prescriptions can be satisfied at a single base curve. See U.S. Pat. No. 6,142,624 (Morris et al.). In general, however, the carrier surface will be of a generic form that allows a range of related lens surfaces to conform to the rimmed aperture outline or eye-wire.
Eyeglass frames usually sit snugly in front of the wearer""s face, being spaced sufficiently therefrom to avoid physical contact whilst being stably positioned. Prescription frames have low curvature along the brow lines, typically equaling the best form base curves required for the most negative lenses of an Rx range. High minus lenses glaze flush with the frame contour and others protrude increasingly as the power is more positive, so that in general, the lens front vertex is located forward of the frame carrier surface. The choice of aperture shapes must allow the height difference between the frame carrier surface and the lens front surface to remain within a tolerance along the lens periphery that is consistent with the typical edge thickness of a lens, e.g. to within about xc2x10.5 mm.
Sunglass frames of the wrap-around form typically have curvature of approximately 6 to 8 D toward the temples. When prescription lenses are fitted, the substance of the inner lens surface intrudes into the space before the wearer""s face. A minus lens protrudes at the temporal limits of the frame aperture, as depicted in FIG. 1a. A plus power flattens the back surface of the lens, intruding against the eyelashes. In practice, wrap-around frames of currently popular styles are consistent with posterior horizontal curves between about 6 and 12 D. This limits the prescription range for an 8 base front surface to within about xe2x88x924 to +2 D, optical design issues apart. Lenses of higher base curve, such as 10 or 12 D for example, offer the potential of a wider prescription range. As shown in FIG. 1b, however, such curves place the lens front vertex outside the design line of popular 8 base design styles and introduce a bug-eyed appearance in the nasal region.
This effect may be eliminated or reduced substantially by using lenses whose front surfaces follow a high base curve in the temporal region and are flattened across the line of sight toward the nasal region. Such lenses may be envisioned as a fusion of the styles of dress eyewear in the forward sense, and of highly wrapped non-corrective sunglasses and shields in a wide-angle sense reaching to the temples. Desirably, they may be glazed into rimmed or partly rimmed frames that are both fashionable and accommodate a range of prescriptions.
It is accordingly a broad object of the present invention to provide rimmed frames, or frames having at least one rimmed portion along the lens aperture, with carrier surfaces having simple and generic topography suited to use with lenses whose front surfaces are of compound design.
By xe2x80x9ccompound designxe2x80x9d and xe2x80x9ccompound curvexe2x80x9d we mean to describe lens surfaces and lenses that have changing base curve across at least one section of the frame or lens aperture, the change in base curve being at least 3 D in a horizontal section and/or 2 D in a vertical section thereof.
By xe2x80x9cbase curvexe2x80x9d we mean the mean curvature, or numeric average of the two principal curvatures of a two dimensional surface as set forth in the CRC Concise Encyclopedia of Mathematics, by E. W. Weisstein, Chapman and Hall, New York 1999, p. 1152. The change in base curve may occur locally on the surface or across an extended region of the surface. Preferably there will be a smooth change in base curve across a substantial portion of the lens aperture as glazed in a spectacle frame.
Another object of the invention is to provide rimmed frames, or frames having at least one rimmed portion along the lens aperture, whose carrier surfaces are of monoformal geometry.
By xe2x80x9cmonoformal geometryxe2x80x9d, we mean standard optical surfaces of conic, cylindrical, spherical, conicoidal or toroidal topography whose cross-sectional curves are of generally quadratic standard form across the frame or lens aperture, thus simplifying manufacture of the frames and also simplifying design modifications of the lens front surface to accommodate optical requirements in a series of lenses to a particular contoured style. By xe2x80x9cmonoformal surfacexe2x80x9d, we mean to describe a cap or dome having a vertex from which it curves equally to either side and symmetry around the vertex that corresponds to a non-closing surface element from an ellipsoid, toroid, cylindroid, sphere or cylinder. Preferably such monoformal surfaces encompass also oblate spheroids and ellipsoids, whose curvature changes monotonically across at least one section of the frame aperture.
In so far as we refer below to the carrier surface being toroidal, ellipsoidal or the like, we mean to specify the symmetry of the solid object from which the surface cap is taken.
By the term xe2x80x9cquadratic standard formxe2x80x9d as used here, we mean a curve belonging to any of the 9 general standard-form quadratic curves as set forth in the CRC Concise Encyclopedia of Mathematics, by E. W. Weisstein, Chapman and Hall, New York 1999, p. 1476, the real space examples of which are straight lines and conic sections.
These and other object and features of the present invention will be apparent from this written description and associated drawings.
In a first aspect of the present invention there is provided a spectacle frame shaped to receive and retain lenses of the wrap-around type having compound design and wherein the edge of the lens is physically retained by a rimmed frame aperture of generally ovaline shape and is located on a monoformal carrier surface, despite the base curvature of the lens changing across at least one section of the lens aperture.
Such frames and the lenses they retain, differ significantly in curvature relationship from frames and lenses known in the prior art.
By the term xe2x80x9clens of the wrap-around typexe2x80x9d, we mean that at least one surface of the optical lens falls on a topographical surface that wraps around the human visual apparatus or forms a facial shield. The topological shape of lenses used in the present invention may be characterized by sagittal depth, which is generally a measure of the three-dimensionality of the lens and lens edge. These depths typically relate to the distance between a vertical plane normal to the line of sight of the lens and the temporal-most edge point and the nasal-most edge point.
In a further aspect, the present invention provides a spectacle frame shaped to receive and retain optical lenses of the wrap-around type wherein the aperture of the lens outline or edge of at least one surface of the optical lens is of generally ovaline shape and exhibits sagittal depth at the horizontal temporal limit that is at least 10 mm greater than the sagittal depth at the horizontal nasal limit. More preferably, the sagittal depth of the lens at the horizontal temporal limit is at least 15 mm greater than the sagittal depth at the horizontal nasal limit.
Preferably, the sagittal depth of the front surface of the glazed lens at its nasal limit will be less than 5 mm, thus maximizing the conformity of the lens and frame to the wearer""s face.
The frame will have sufficient curvature and length in the horizontal direction of its datum line to enclose a wide visual field and afford physical protection to the wearer""s eyes. Its forward location, curvature and length from datum center to the nasal edge of the datum line and the upper and lower ends of the vertical primary meridian will avoid physical clash with the wearer""s face and eye lashes. Suitable frames exhibit lens aperture shapes that are relatively broad in the field of forward vision and taper steadily towards the temples, conforming to the human facial structure.
By the terms xe2x80x9clensxe2x80x9d as used herein we mean a cut or shaped-edge optical or ophthalmic lens.
The optical lens may be removably or permanently attached to the frame. It may provide a corrective prescription in a range of minus or plus powers or may be plano, and, in some embodiments, is suitable for industrial safety or contact sport applications.
The spectacle frame according to aspects of the present invention may be rimmed, or partially rimmed, allowing the lens elements to be retained securely in front of the wearer so that the optical design axes of the lens elements may be held closely parallel with the wearer""s direct line of sight in distance vision and aligned according to the interpupillary distance of the wearer.
By xe2x80x9coptical design axisxe2x80x9d as used here, we mean the axis intended by the lens designer to be aligned with the wearer""s direct line of sight. This may not coincide with the optical axis of the optical lens element if, for example, the lens is designed specifically to be tilted or decentered as a means to enhance wrap toward the temples. Such lenses typically bear surface corrections to compensate for their intended orientation.
The aperture outline of a spectacle frame is usually represented by its projection on the vertical frontal plane of the lens. Its definition requires four datum points spaced on the front surface of the lens periphery and one additional condition specifying the frame carrier surface. Convenient datum points are the four points of intersection of the lens periphery with the horizontal xe2x80x9cequatorxe2x80x9d and vertical xe2x80x9cprime meridianxe2x80x9d lines through the lens front vertex. We represent these in coordinates originating at the lens front vertex. The lens front and the frame carrier surface must conform closely at the four datum points, and these surfaces should be confluent within allowed tolerances (say xc2x10.5 mm) along the aperture outline, although they may be quite separate elsewhere across the aperture. The final condition locates the lens front vertex relative to the frame carrier surface.
In order to facilitate discussion of the geometrical relationships involved, we now define a series of simple surfaces that specify particular aspects of the compound lens surface, specifically one that has increasing curvature from a nasal region to a temporal region:
The xe2x80x9csteepest internal bounding surfacexe2x80x9d or xe2x80x9cinternal boundaryxe2x80x9d is the specific toroidal, spherical or cylindrical surface that intersects the four datum points at the lens front periphery and is co-tangential with the lens front surface at the nasal limit;
The xe2x80x9cmean slope surfacexe2x80x9d is the specific toroidal, spherical or cylindrical surface that intersects the four datum points at the lens front periphery and has equal differences in slope relative to the lens surface at both the nasal and temporal limits;
The xe2x80x9cmean height surfacexe2x80x9d is the specific toroidal, spherical or cylindrical surface that intersects the four datum points at the lens front periphery and also the lens front vertex; and
The xe2x80x9cshallowest external bounding surfacexe2x80x9d or xe2x80x9cexternal boundaryxe2x80x9d is the specific toroidal, spherical or cylindrical surface that intersects the four datum points at the lens front periphery and is co-tangential with the lens front surface at the temporal limit.
For spherical, cylindrical and toroidal lenses, all of the above surfaces are coincident and are exactly the lens front surface. Prior art prescription spectacle frames and dual lens sunglass frames position the optical lenses in the frame so that each lens front vertex is located on its respective frame carrier surface, or is located forward away from the wearer. The analogous principle for compound design lens surfaces would be to locate the frame carrier surfaces at the mean height surface or rearward thereof. However, there is a continuous perimeter of intersection between the frame carrier surface and the lens front surface only when the two are spaced apart, for example when the frame carrier surface is near to or behind the inner boundary surface. This configuration places the lens front vertex forward of the frame carrier surface analogously to the prior art. But, we have found that the aperture shapes allowed by the confluence of the surfaces along their perimeter of intersection do not enclose the wearer""s visual apparatus as required. The corresponding aperture shapes taper nasally and do not surround the field of forward vision.
The geometry of compound design surfaces is distinguished by the presence of separated inner bound and external bound surfaces. These are depicted in FIG. 3a, where: Curve 1 is a horizontal section of a compound design surface; Curve 2 is the external bound surface merging tangentially at the temporal limit T; and, Curve 3 is the internal bound surface merging tangentially at the nasal limit N. Frames that utilize the face conforming geometry of compound designs and also allow desirably shaped apertures, surrounding the field of forward vision and tapering toward the temples, place the frame carrier surface near to the external boundary surface or forward thereof. Such frames locate the lens front vertex rearward of the frame carrier surface. The arrangement is depicted schematically in FIG. 3b. 
In another aspect, the present invention provides a rimmed spectacle frame shaped to receive and retain lenses of the wrap-around type wherein each aperture of each lens"" outline or the edge of at least one surface of each lens is of generally ovaline shape enclosing the forward field of vision and conforming with facial form toward the temples, and wherein the frame apertures are designed to generally spherical, cylindrical or toroidal carrier surfaces (monoformal surfaces) that are always more highly curved than the lens mean height surface, so positioning the lens front vertex rearward of its respective frame carrier surface.
In a preferred form, the lenses are retained securely by one or more rimmed sections of arcuate frame apertures each following the frame carrier surfaces. These sections may be interrupted by unconstrained segments of the lens periphery edged so as to improve conformity of the glazed spectacles to the nose and/or brows, or to accentuate the outline of the lens in the vicinity of the temples or cheek line.
Greatest freedom in the selection of aperture outline shapes occurs when the frame carrier surface and the lens front surface merge intimately in the vicinity of their true intersection path. In this case, the frame carrier surface must be close to the shallowest surface that bounds the lens front surface externally while intersecting the established datum points, the xe2x80x9cexternal boundaryxe2x80x9d.
In a still further aspect, the present invention provides a rimmed spectacle frame, shaped to receive and retain lenses of the wrap-around type, wherein the apertures of the lenses outline or edge of at least one surface of each lens is of generally ovaline shape enclosing the forward field of vision and conforming with facial form toward the temples, wherein the frame apertures are each designed to a generally spherical, cylindrical or toroidal carrier surface that is closely proximate the shallowest surface that bounds the lens front surface externally while intersecting the frame datum points.
The foregoing is intended only as a summary of this disclosure, the scope of the invention being determined by the literal language of the claims and equivalent thereof.